DC-to-DC converters typically convert power from one DC voltage to another DC voltage. They are usually regulated devices, taking a possibly varying input voltage, and providing a stable, regulated output voltage, often up to some current (amperage) limit.
This basic DC-to-DC conversion functionality makes DC-to-DC converters widely used for power conversion in many electronic systems, such as communications systems, among others. In this way, DC-to-DC converters can in some instances be thought of as a “black box” that receives one voltage from our nation's power grid or a battery, for example, and converts it to another voltage that is used to power an integrated circuit.